In recently years, as the global trend of aging society, the demand of medical assist devices is gradually increased. For the reason, a variety of medical assist robots are developed, such as exoskeleton robot, surgical robot, rehabilitation robot and the like. In general, joints in these robots are driven by rotatory actuator module, which is composed of motor and gearbox, and provides appropriate rotational speed and torque output. The protection mechanism is also very important for these actuator modules, especially for rehabilitation applications. For the module, too much power or higher stiffness will easily cause patient harm, but too little power or higher compliance will not be able to drive the required motion. How to achieve an active compliance control which can adjust the actuator module from stiff to compliant operation is a key issue in medical assist devices.
Power coupling technique is one of methods to realize active compliance control. Output power from two motors are coupled by at least one differential gear set, where one of the motors provides positioning function, so-called position motor, and the other provides stiffness adjustment function through manipulation of its torque output, called stiffness motor. During operating, position of the actuator module is controlled by position motor, and stiffness is by the stiffness motor. Both position control and torque control algorithm is able to be performed on each motor by a typical motor controller, and therefore the compliance of actuator module can be achieved by varying torque output on stiffness motor. However, in previous design, extra housings or mounting structures are required to couple two motors and the differential gearbox, which will significantly increase total size of the actuator module; as the consequence, the conventional two motors design is not suitable for portable applications, especially for the portable assist devices.
In general, this two motors design, called dual-motor structure, can be classified into two types, including series-connected dual-motor structure and parallel-connected dual-motor structure. For example, Taiwan Patent Publication No. I274460 disclosed a series-connected dual-motor structure, which connects two motors to a planetary gear set in series. The planet carrier and the ring gear of the planetary gear set are driven by two motors, respectively. The coupled power is outputted from the sun gear of the planetary gear set. This series-connected type is relatively narrow in outside diameter than parallel-connected type, but its length is significantly increased. This increased length causes difficulty of mechanical design, and increasing its overall size. U.S. Pat. No. 7,538,466 also has the same difficulties.
Taiwan Patent Publication No. I292650 disclosed a parallel-connected dual-motor structure, in which two motors are arranged side by side, and connected to a planetary gear set. This parallel-connected type is shorter than series-connected type, but its outer dimension is wider in these two types, which also causes similar difficulties in mechanical design.
Therefore, to provide an actuator module having compliance manipulation ability and compact size become an important issue.